Campaign, voucher, standalone voucher

docs/guides/getting_started/Key-Concepts.md

@@ -16,23 +16,41 @@ Voucherify operates on fundamental building blocks which you can use to create y
 
 A campaign is a basic entity in Voucherify that is used to carry out promotional activities. 
 
-[Campaign object reference](ref:get-campaign)
-
-Voucherify supports five basic campaign types:
+There are five basic campaign types, which create:
 - [discount coupons](doc:discount-effects),
 - [gift vouchers](doc:prepaid-gift-cards),
 - [referral codes](doc:referral-program),
-- [promotion](doc:stacking-promotion-tiers),
-- [loyalty program](doc:loyalty-program).
+- [promotions](doc:stacking-promotion-tiers),
+- [loyalty cards](doc:loyalty-program).
 
-<!-- Fix links here -->
+Go to [campaign API reference](ref:campaign-object) to learn more about the campaign object.
 
 ### Voucher
 
-### Promotions and promotion tiers
+A voucher is an entity in Voucherify that is used as an incentive for end-customers to make a purchase. Every voucher has a unique code and id. <!-- Vouchers are assigned to customers. -->
+
+A voucher is used in the following types of campaigns as:
+- [discount coupons](doc:discount-effects),
+- [gift vouchers](doc:prepaid-gift-cards),
+- [referral codes](doc:referral-program),
+- [loyalty cards](doc:loyalty-program).
+
+Go to [voucher API reference](ref:voucher-object) to learn more about the voucher object.
+
+<!-- TBD: how much more info? code format? qr/barcodes? other info from building blocks? -->
 
 ### Standalone voucher
 
+A standalone voucher is an entity in Voucherify that is used as an incentive for end-customers to make a purchase. Every standalone voucher has a unique code and id. 
+
+Unlike regular [vouchers](#voucher), standalone vouchers are represented by a single code and cannot be assigned to individual customers. Standalone vouchers are designed for multiple use by many customers.
+
+Go to [voucher API reference](ref:voucher-object) to learn more about the voucher object.
+
+### Promotions and promotion tiers
+
+A promotion is a campaign in which a discounts to a customer's cart without promo codes. Once a customer qualifies for a promotion, the discount is automatically added to their cart. 
+
 ## Incentivization
 
 ### Validation rules